Activation of the hedgehog (Hh) pathway, originally identified in fruit fly Drosophila, occurs in basal cell carcinomas (BCCs), gastrointestinal, prostate, breast and lung cancers. Environmental carcinogens are major risk factors for these cancers. The 7-transmembrane smoothened (SMO) is a key signal transducer of the Hh pathway, whose function is inhibited by the 12- transmembrane protein Patched (PTC) in the absence of Hh ligand. Hh signaling proceeds via binding of Hh ligand to its receptor, transcriptional factors. Gli transcription factors are responsible for Hh target gene expression. Little is known about signaling events from SMO to Gli transcriptional factors in vertebrates. For example, how SMO signaling is regulated, what are the molecular events that link SMO to downstream signaling, how does Hh signaling contribute to carcinogenesis? We have made significant progress to elucidate these issues. Most notably, we were the first group linking the Ran GTPase- binding protein, RanBPM, to the Hh signaling pathway. Our data indicate that RanBPM associates with SMO and regulates SMO signaling. Based on our data, we hypothesize that RanBPM is a novel component in the Hh pathway and is required for Hh signaling-mediated carcinogenesis. We will pursue three specific aims to test our central hypothesis and accomplish our objectives. First, we will determine the molecular basis of SMO-RanBPM interaction (Aim 1). Second, we will identify the mechanisms by which RanBPM facilitates SMO signaling (Aim 2). Third, determine the in vivo significance of RanBPM in Hh signaling-mediated carcinogenesis (Aim 3).Health relevance: Hedgehog signaling is frequently activated in human cancers, including most basal cell skin cancers and nearly a third of non-skin tumors. A large proportion of these tumors are caused by environmental carcinogens, such as UV irradiation, auto exhaust fumes and asbestos fibers. The emerging role of Hh signaling in different cancer types further emphasizes the relevance of studying this pathway to human health. Determining the mechanisms of signal transduction in this pathway, the long-term goal of this project, will have widespread clinical implications for cancer control. Identification of the novel SMO associated protein, RanBPM, provides a unique opportunity for us to dissect Hh signaling in human cancers.